Vision is achieved in the human eye by transmitting an image through a clear outer portion called the cornea, and focusing this image via a natural lens onto a retina. When the natural lens looses its ability to clearly focus the image onto the retina through, for example, cataracts or injury, the quality of the focused image on the retina can be severely compromised.
An accepted treatment for a damaged natural lens is surgical removal of the natural lens and replacement of the natural lens with an artificial intraocular lens. One way to accomplish this procedure is to form a relatively long incision in the eye and remove the natural lens in one piece. A more popular method for removing the natural lens is to form a shorter incision in the eye and insert a probe or a phaco tip of a phacoemulsification instrument through the incision into the eye to break up the natural lens using ultrasonic energy. The lens fragments can then be aspirated from the natural eye through the relatively short phaco incision, and the phaco tip is then removed.
A preferred conventional method of removing a natural lens is accompanied with a subsequent implantation of a replacement intraocular lens in the same surgical procedure. A typical intraocular lens includes an optic usually having a diameter of about 6 mm, and fixation members coupled to (or formed with) the optic to fix the optic within the eye in the region of the extracted natural lens. These fixation members are generally in the form of at least two haptics, which may be flexible, elongated, open-ended loops that project from the edge of an optic portion of the intraocular lens. The fixation member may require additional incision links, depending upon the number, length, and configuration of the fixation member.
Another construction of the artificial lens is a plate or disk lens where the optical portion is part of the solid lens body and the lens fixation is provided by the proper dimensions of the lens body. No fixation members in the form of loops are involved.
Intraocular lenses can be of two basic types, those having a hard or rigid optic formed, for example, of polymethylmethacrylate (PMMA) and those having a deformable optic which is constructed of a deformable material such as silicone, hydrogel, or an acrylic. When a hard intraocular lens is used, the small phaco incision must be enlarged to approximately the diameter of the hard optic, in order to permit the hard optic to be inserted through the incision. A deformable optic, on the other hand, may have a high elongation so that the optic can be caused to resiliently stretch and flex to assume a small cross-sectional configuration for passage through a small phaco incision.
Before implanting the intraocular lens, the physician must determine the intraocular lens power needed to achieve the desired refraction needs of the patient. This procedure can be difficult and inexact.
Errors in measurement, inaccuracy of lens position assumptions, and the difficulty of achieving precise placement of an intraocular lens make the physician's selection of an exact corrective power prone to inaccuracies. Post-operative changes to the patient's eye may also change the final refractive error of the patient. Consequently, the intraocular lens, after implantation, can yield significant refractive error. These post-operative refractive errors must sometimes be corrected by a subsequent surgery to replace the implanted intraocular lens with another intraocular lens. A subsequent surgery involves re-entry into the eye through a new incision, removal of the initial intraocular lens, and implantation of a new intraocular lens. Needless to say, this conventional subsequent surgery procedure can be traumatic to the eye. Introduction of the multifocal and toric intraocular lenses further increases the requirement to achieve the refractive goal of a cataract surgery.
One approach for limiting the amount of trauma on the human eye caused by subsequent replacement of the intraocular lens is disclosed in Patel U.S. Pat. No. 5,366,502. This patent discloses supplemental intraocular lenses which may be subsequently attached to primary intraocular lenses after the initial implantation of the primary intraocular lens. Addition of a supplemental intraocular lens to a primary intraocular lens does not entail removal of the primary intraocular lens, and further requires a relatively small incision in the eye. The supplemental intraocular lenses, and most of the primary intraocular lenses, of this patent include specially configured connectors for mating the supplemental intraocular lens to the implanted, primary intraocular lens. These connectors can be in the form of hooks, projections, slots, and loops, which are suitable for securing the supplemental intraocular lens to the primary intraocular lens. These various securing means, however, can be complex and difficult to manufacture and implement. Additionally, the sizes of these supplemental intraocular lenses are often unnecessarily large, thus requiring a larger incision and more trauma to the eye.